This disclosure relates to a guard door monitoring system comprising a guard door as an entrance to a safety area, a guard door monitoring module for monitoring a state of the guard door, wherein the guard door monitoring module has an actuator and a sensor, which can be brought into interaction with one another in an electrically contactless manner and thereby generate a guard door signal, and a control unit, which is configured to analyze the guard door signal and to control a machine or system located in the safety area depending on the guard door signal.
The applicant markets a guard door monitoring module of the above-mentioned type under the name “PSENslock”, which can be used in a versatile manner and is suitable for applications up to the highest security level PL e (Performance Level e according to ISO 13849-1). A detailed product documentation regarding this product is available on the homepage of the applicant (http://www.pilz.de; Application Note—No. 1002459_DE_01 of 06.02.2012).
Guard door monitoring systems of this type are used on guard doors that are intended to prevent access to a machine or system working in an automated manner, provided the machine or system is located in a dangerous state. The access to these machines or systems can also be granted just as well via protective flaps, hoods and pivoting or sliding doors. These entrances are also to be understood as guard doors in the present context.
In order to prevent an operator from reaching the working or safety area during a dangerous machine movement, the safety area is often separated off from the outside world by a protective housing. The access to the safety area is then usually only possible through one or more guard doors in the protective housing.
Machines or systems in which protective housings of this type are used for example include robots, machine tools with a rapidly rotating spindle, transport or conveying systems, presses or other machines and systems of which the operation poses a risk to people located in the working range of the machine. Guard door monitoring modules provided on guard doors can be used as signaling devices, with the aid of which a control device can identify the closed state of the guard door. The control device is configured to enable start-up of the machine or system only when the guard door is closed. If the guard door is opened (if possible) during running operation, the control device must bring the machine or system into a safe state, in which for example the power supply to the machine or system is switched off.
There are a large number of machines and systems that still pose a risk for a certain time even after the switch-off, for example because the machine or system still continues to run. This time is also referred to as the run-down time of the system. In these cases special guard door monitoring modules and/or safety switches are required. Such safety switches prevent the guard door from being opened until the machine system has reached its safe state. This function is referred to as locking of the guard door.
The known safety switches conventionally have what is known as an actuator, which is arranged on the movable guard door. When the guard door is closed the actuator engages with an actuator receptacle on the door frame, which is detected with the aid of one or more sensors. In the case of a safety switch with locking, the actuator is additionally blocked in the actuator receptacle against removal. The actuator in this case thus performs two functions, specifically on the one hand it acts as a detector element, with the aid of which the closed position of the guard door can be detected, and on the other hand it acts as a bolt, which prevents the guard door from being opened as long as the actuator is blocked in the actuator receptacle. The locking can be provided for example via an actuator driven by an electric motor or via an electromagnetic actuator, which is actuated by the control device until the monitored machine or system has reached the safe state thereof.
An example for such a safety switch with locking system is also disclosed in EP 1 430 497 A1.
However, the above-described locking on the guard doors do not always have to perform only safety-relevant functions, such as the prevention of access to the safety area during the run-down time of the system. Lockings are also often used as process protection. In this case the locking prevents an accidental system interruption by the operator. Although a locking in some cases of application is not necessary from safety viewpoints, it then at least prevents an accidental interruption of the production process. Since a renewed start-up of the system may be complicated and time-consuming depending on the complexity of the system, important production time and therefore also production costs can be saved by such a process protection. It goes without saying that the above-described guard door monitoring modules, which are also referred to as safety switches, can also be used combined as process protection with safety-relevant function.
Irrespective of whether safety switches with or without locking are used on the guard doors, problems often occur in practice as a result of incorrect operation and intentional or unintentional manipulations of the safety devices. A manipulation protection of these safety and monitoring systems is therefore of immense importance. However, safety gaps may also sometimes occur unintentionally due to incorrect handling on the part of the operating staff and must be prevented at all costs. For example, in the case of the above-mentioned guard door monitoring systems, there could be a situation in which an operator gains access to the system, wherein the system is duly switched off as the guard door is opened. However, if a second operator now does not notice the first operator in the safety area, closes the guard door again and starts the system, this could lead to a significant safety risk of the first operator within the system. Such a situation is conceivable in particular in very large systems into which it is difficult to see.